Rechargeable units are becoming more and more popular as the battery quality is increasing. A number of different charging systems are known, but they generally all require that the battery is dismounted from the unit, that the unit is changed directly through a male and female plug and socket system or that the unit is placed in a cradle during charging with the result that the unit cannot be used for extended periods at a time. Thus, there is a need for a charging system which provides a rechargeable unit which is truly useable during charging.
From U.S. Pat. No. 5,459,389 a dual charging system is known. The system comprises a battery pack and a charger unit, which may be recharged by either plugging directly into a power main or by placement in the charger unit. The charging unit is a flat structure with a slight depression for receiving the battery pack which requires that the charging unit is equipped with hooks to keep the battery pack properly positioned in the charger unit. These hooks however, make the positioning of the battery pack in the charger unit more complicated as a specific insertion angle and twisting movement required to position the battery pack. Also, the movement needed to remove the battery pack from the charger unit is complex, which makes the action slow in order not to risk damaging the hooks. Furthermore, the insertion of the battery pack into the mains requires that a set of prongs are extended from the battery pack housing, which requires that the positioning of the battery pack is performed rather slowly in order to be sure that the prongs are extended the correct amount or else there is a risk that the battery pack will not be recharged. Additionally the retractable prongs make the battery unit complex and thus more prone to failure.
US 2007/0090789 describes a mobile device with dual charging ports. The device can be charged by a plug or by insertion in a charging seat. When recharged by the charging seat, the device specifically needs to be inserted along a predetermined direction in order-to engage with the conductive terminals of the charging seat. Further there is an eminent risk that the conductive terminals will be damaged due to their design and placement perpendicular to a possible direction of insertion. Also, once the device is inserted it is not possible to see if the device is properly inserted to achieve electrical contact with the conductive terminals.
Thus there is also a need for a system allowing reliable charging of a rechargeable unit under a variety of conditions. The unit must be easy to use and be sturdy and reliably even when used with swift movements.